Electromechanical transducer employing piezomagnetic manganese ferrous ferrite



March 1968 F. G. BROCKMAN ETAL 3,375,195

ELECTROMECHANICAL TRANSDUCER EMPLOYING PIEZOMAGNETIC MANGANESE FERROUS FERRITE Original Filed Sept. 50, 1963 INVENTORS. IRANKG. BROCIQVIAN PAUL W BECK Manna C IENECK United States Patent 3,375,195 ELECTROMECHANICAL TRANSDUCER EM- PLOYING PIEZOMAGNETIC MANGANESE FERROUS FERRITE Frank G. Brockman, Dobbs Ferry, Paul W. Beck, Irvington, and Walter G. Steneck, Ossining, N.Y., assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware v Continuation of application Ser. No. 312,687, Sept. 30, 1963. This application Nov. 14, 1966, Ser. No. 594,255 1 Claim. (Cl. 252--62.56)

ABSTRACT OF THE DISCLOSURE A manganese-ferrous ferrite core suit-able for use in an electromechanical transducer; The core has a coupling coefii'cient of 30% or more. The core is prepared by mixing manganese and ferric oxides in proportions corresponding to the composition of the core, followed by prefiring the mixture, molding cores, and sintering and cooling in atmospheres in which the ratio of carbon dioxide to carbon monoxide is adjusted to result in the formation of an amount of ferrous oxide corresponding to the amount of ferrous iron in the composition.

This is a continuation of application Ser. No. 312,687, filed Sept. 30, 1963, now abandoned.

Our invention relates to ferromagnetic materials and more particularly to those having piezomagnetic properties, and methods of making the same.

Such materials are useful in vibrators for converting electrical energy into mechanical energy, for example ultrasonic vibrations, and conversely for converting mechanical energy to electrical energy (see for example, Philips Technical Review, 1 8, 258-298, 1956/57). It is desirable for such purposes that the material have a large electromechanical coupling coefiicient which is a measure of the conversion of magnetic energy into mechanical energy (or vice versa). Known ferromagnetic materials having piezomagnetic properties, viz nickel-cobalt ferrites, generally exhibit a coupling coefiicient in the neighborhood of 20%.

A principal object of our invention is to provide a new and novel material having piezomagnetic properties which has a large electromechanical coupling coefiicient and is thus more eflicient in converting electrical to mechanical energy and vice versa.

Another object of our invention is to provide a method of making a piezomagnetic material having a large electromechanica-l coupling coeflicient.

A further object of our invention is to provide a new and novel material having piezorn'agnetic properties which has a coupling cefiicient exceeding 30%.

These and further objects of the invention will appear as the specification progresses.

In accordance with our invention, this new and novel ferromagnetic material, which exhibits piezomagnetic properties with a large electromechanical coupling coefiicient, is a manganese ferrous ferrite having a composition:

For coupling coefiicients of 30% or more, x=0;28 to 0.67.

It has been generally considered that manganese ferrites of high permeability are practically devoid of magnetostrictive effects. It was widely considered that the high permeability was the result of a near zero in magnetostriet i'on brought about by the cancellation of negative magnetostrict'ion. of manganese ferrites by the appropri- 3,375,195 Patented Mar. 26, 1968 ate amount of ferrous ferrite of positive magnetostriction. (See, for example, Ferrites by J. Smit and H. P. ll. Wi-jn, 1959, p. 17 1.) One would therefore expect that high permeability mixed manganese ferrites, e.g. manganeseferrous fer-rite, would be devoid of piezomagnetic effects, and in particular would have a small electromechanical coupling coefiicient. However, we have found quite unexpectedly that manganese ferrous ferrites of the type do have piezomagnetic properties and that for a range of compositions in which x has a value between 0.28 and 0.67,- thecoupling coeflicient is at least 30%.

The invention will be described with reference to the accompanying drawing, the sole figure of which shows the electromechanical coefficients of the system MH FC F 62 04 The efficiency of a ferromagnetic transducer converting magnetic energy to mechanical energy, and vice versa, is determined by its electromechanical coupling coefiicient k, which is a quantity related to the stored mechanical and magnetic energies. It is defined as the square root of the ratio of the converted stored energy to the input stored energy for the case of no losses or radiation. For maximum conversion of energy, and vice versa, this coeflicient should be as large as possible, i.e. approach unity, or

The coupling coefiicient k has a maximum value as a function of bias field at any one temperature. This maximum in k, however, may be observed under two different conditions: (1) in the case when the sample is initially demagnetized and k is observed with values of the bias field increasing from zero, and (2) in the case when the sample is in the remanent state and k is observed with values of the bias field increasing from zero. In case (1), k begins at zero for H =0. In case (2), k begins at k from H =0 and has a maximum value k Referring then to the drawing, the values of k and k are plotted as ordinates and values of x in the composition Mn Fe Fe O as abscissae. It will be seen that the coupling coefiicient k exceeds 30% over the range x=0.28- to 0.67. Beyond a value of x=0.7, the coupling coefiicient k drops rather abruptly so that the range of interest appears to coincide with a coupling coefl i'cient of at least 30%.

The following examples are illustrative of the method of manufacture of manganese ferrous ferrites' according to the invention:

Example 1 Milo AF0 1 6 0; The following reactants were weighed out:

Grams Iron oxide (F6203), 100.0% Fe O 166.09 Manganese oxide (M11 0 99.88% Mn O' 25.29

These oxideswere thoroughly mixed with 300 cc. ethanol in a high speed blender for 30 minutes. The slurry was dried under infrared lamps; the cake resulting was broken up and drying was completed at C. for about I or 2 hours. The dry material was broken up in a mortar and pestle and passed through a Sieve, US.- Standard Sieve No. 30. This sieved powder was loaded into an Alundum boat and the boat and load were placed in an atmosphere furnace for prefiring.

Beginning at room temperature, theatmosphere in the furnace was CO /CO: lO/l by volume. This ratio CO /CO was maintained up to a temperature of about 3 600 C. From 600 C. to 800 C. the ratio was change at 100 C. intervals as follows: I

Degrees C.:

v 600 to 700, CO /CO 14/1 700 to 800, CO /CO 18/1 800, CO /CO 24/1 The powder was maintained for about 15 hours at 800 C. under the 24/1 atmosphere. I

In cooling, the CO /CO ratio was controlled in the same way as with rising temperature,

. Degrees C.:

800 to 700, CO /CO 18/1 700 to 600, CO /CO 14/1 600 to room temperature, CO /CO 10/1- Degrees C.:

600 to 700, CO /CO 14/1 700 to 800, CO /CO 18/1 800 to 900, CO /CO 24/1 900 to 1000, /00 32/1 1000 to 1100, CO /CO 42/1 1100 to 1200, CO /CO 56/1 1200 to 1250, CO /CO 75/1 Test toroids were maintained at 1250 C. for 2 hours under the 75/1 CO /CO atmosphere. Cooling followed the same program as the heating.

The test rings were about 0D. 2.8 cm., I.D. 2.0 cm., height 0.67 cm. These resonated in the radial mode at about 70 kc./sec. The electromechanical coupling co- 'efficient was measured by the resonance method and was found to be 32.7% at the optimum bias field of zero oersted (i.e. at remanence).

Example 2 0.5 o.5 2 4 The following reactants were weighed out:

Grams Iron oxide F6 0, 100.0% Fe O 159.70 Manganese oxide (Mn O 99.88% Mn O 31.61

The procedure was the same as in Example 1 up to the prefiring. Prefiring of the powder was carried out as follows:

Beginning at room temperature the atmosphere in the furnace was CO /CO 11/1 by volume. This ratio of CO /CO was maintained up to a temperature of about 600 C. From 600 C. to 700 C. the ratio-CO /CO was 15/1. At 700 C. the ratio was changed to 20/1. The powder was kept at 700 C. under CO /CO: 20/1 for 22 hours. In cooling the CO /CO ratio was changed in the same Way as with rising temperature.

I The prefired powder was prepared in the same manner as in Example 1 and test toroids Were pressed and fired.

The firing cycle was as follows:

From room temperature to 600 C., CO /CO 11/1 and from:

Degrees C.:

600 to 700, CO /CO 15/1 700 to 800, CO /CO 20/1 800 to 900, CO /CO 27/1 900 to 1000, CO /CO 36/1 4 1000 to 1100, CO/CO 46/1 1100 to 1200, CO /CO 61/1 1200 to 1250, CO /CO 81/1 The toroids were maintained for two hours at 1250 C. under the 81/1 CO /CO atmosphere. Cooling followed the same program as the heating.

The test rings were about the same size as those in Example 1. They resonated in the radial mode at about ke./sec. The electromechanical coupling coefficient was measured by the resonance method and was found to be 39.1% at the optimum bias field of zero (oersted) (i.e. at remanence).

Example 3 o.s o.4 z 4 The following reactants were weighed out:

Grams Iron oxide (Fe O 100.0% Fe O 153.31 Manganese oxide (Mn O 99.81% Mn O 37.94

The procedure was the same as in Example 1 up to the prefiring. Prefiring of the powder was carried out as follows:

Beginning at room temperature, the atmosphere in the furnace was CO /CO 13/1 by volume.

This ratio was maintained up to a temperatureof about 600 C. From 600 C. to 700 C. the ratio was 17/1. At 700 C. the ratio was changed to 23/1. The powder was kept at 700 C. under CO /CO 23/1 for 22 hours. In cooling, the CO /CO ratio was changed in the same way as with rising temperature.

The prefired powder was prepared in the same manner as in Example 1 and .test toroids were pressed and fired.

The firing cycle was as follows.

From room temperature to 600 C., C'O /CO 13/1 and from:

600" to 700 C., CO /CO 17/1 700 to 800 C., CO /CO 2.3/1 800 to 900 C., CO /CO 30/1 900 to 1000 C., co /c0 40/1 1000 to 1100 C., CO /C'O 50/1 1100 to 1200 C., CO /CO h 67/1 1200 to 1250 C., CO /CO 88/1 quired, We do not wish to be restricted to the atmospheres given in the examples. In order to illustrate this, we give: an additional example. In this example the composition was the same as given in Example 3, but the firing atmosphere was more oxidizing.

Example 4 The preparationof the materials for this example was essentially the same as that of Example 3 up to the fina firing of the test toroids.

In this example, the test rings were fired from room temperature to 1300 C. under an atmosphere, at all times, of pure CO and cooled also under the same at mosphere. I

The test ring was about OJD. 2.8 cm., I.D. 2.0 cm., height 1.3 cm. It resonated in the radial mode at about 70 kc./sec. The electromechanical coupling coefiicient was" 5 measured by the resonance method and was found to be 42.0% at the optimum bias field of 7.5 oersteds.

While We have carried out the firing in the examples in atmospheres of CO and CO, this atmosphere is not required since it has been found that it is only essential to the preparation of such ferrites that the partial pressure of oxygen in the atmosphere employed during the final firing should lie between 10- and 10 atmosphere. Thus, atmospheres of technical nitrogen, or noble gases containing oxygen at a partial pressure of 10- to 10 atmosphere may be employed.

Therefore, while we have described our invention in connection with specific examples and applications thereof, other modifications will be readily apparent to those skilled in this art Without departing from the spirit and scope of the invention which is defined in the appended claim.

What is claimed is:

1. In a vibrator for converting electrical energy into mechanical energy and vice versa, a core having a coupling coefficient of at least 30% and consisting essentially of a composition:

Mn Fe Fe O x having a value between 0.28 and 0.67.

References Cited UNITED STATES PATENTS 2,636,860 4/1953 Snoek et a1. 25262.5 3,027,327 3/1962 Blank 252-62.5 3,047,429 7/1962 Stoller et a1. 25262.5

OTHER REFERENCES Brailsford: Magnetic Materials, 1960, p. 169. Smit and Wijn: Ferrites, 1959, pp.2545.

TOBIAS E. LEVOW, Primary Examiner.

20 R. D. EDMONDS, Examiner. 

